A hydraulic system QDC (Quick Disconnect Coupling), comprised of operatively connected nipple and coupler assemblies, provides for ease of maintenance when servicing an aircraft or a vehicle. Such QDCs permit the removal/replacement of associated equipment with minimal or preferably no loss of hydraulic fluid.
Existing, commercially available, Thread-Lok QDCs provide today's aerospace and other critical fluid handling systems with quick disconnect capabilities, self-sealing action and visual/touch indication of fully coupled positions. Such Thread-Lok couplings offer simple one hand operation as well as reliable performance during the maintenance of fluid handling systems. These thread-together couplings provide the mechanical advantage required for coupling under higher pressures.
One of the more difficult challenges that QDC manufacturers face today is the ever increasing demand for such couplings to be resistant to onboard fire during flight or operation. Existing industry specifications, including AS 1055, establish test criteria for couplings to be fire resistant and even fire proof. During a fire resistance test, the QDC is exposed to flame temperatures of over 2000 degrees F. and must be able to contain leakage satisfactorily at the coupling's normal internal pressure and flow rate for a minimum of five minutes. In order to be considered fire proof, a QDC must pass the same test conditions, but for a minimum of fifteen minutes. A key parameter for such couplings to pass this test is the ability of the internal fluid flow to carry away the heat generated and subsequently transferred by the flames. Today, many end users are now even requesting QDCs that can pass this test at normal operating pressures without the benefit of any internal fluid flow.
The noted problem has been addressed in the prior art and a fire resistant sealing ring combination is set forth in U.S. Pat. No. 3,869,132 to Taylor et al., and involves the use of a metallic static seal “C” ring. While the concept of the use of an elastomeric seal for providing the main sealing feature under normal operation and the use of a metal seal during a fire is similar to the QDC of the present invention, the present invention involves the use of a radial type seal, unlike that of this reference which involves the use of a face seal design. The metal “C” ring and other variations set forth in this reference require substantial force for actuation and cannot be readily adapted for use in quick disconnect applications since this type of metal seal requires not only substantial force to operate but also has a narrow functional scope.
U.S. Pat. No. 4,269,389 to Ekman, while pertaining to a quick disconnect device, uses sealing philosophies that are vastly different from those of the present invention. Similarly, while the structure set forth in U.S. Pat. No. 5,845,945 to Carstensen, in FIG. 3, pertains to a metal wedge back-up ring seal and an O-ring similar to that of the present invention, the concept is used in this reference is used in a single connection application mechanism that allows the connection of two tubes and does not contain a feature for the removal of the two tubes as is typical in a QDC and thus represents a totally different application. The noted arrangement of the seal and back-up ring is solely to eliminate the gap between the tapered female member and the tapered male member due to tolerances and thus functions only to provide sealing but does not include a fire resistant function.
While the structure of U.S. Pat. No. 6,173,968B1 to Nelson et al. includes a metal wedge back-up seal an O-ring arrangement similar to that of the present invention, the back-up ring has only one wedge angle that causes the back-up ring to block the extrusion gap formed between the male and female members. In contrast, the present invention seal ring utilizes two angles, with the additional angle allowing for increased force between the two parts and also includes a secondary back-up seal ring of a high strength and high temperature-resistant material. The noted reference design only operates up to about 500 degrees F. as compared with that of the present invention which has to operate in fire environments that have temperatures as high as 2250 degrees F. A key feature in this reference is that it utilizes a relatively large extrusion gap whereas in the present invention the extrusion gap is deliberately kept small.
The structure set forth in WO 89/01586 to Millard is again intended for connecting together two pipes. The noted coupling is unlike a standard QDC that can be coupled without requiring any tools. This reference requires the parts to be bolted together and the seal design is different from that of the present invention. Similarly, the structure of U.S. Pat. No. 3,612,577 to Pope et al., involves concentric pipes that uses multiple static seals with supporting back-up rings. This differs from the present invention in that the reference structure does not provide a coupling function. The only item of relevance is that the metal back-up ring has the form of a wedge. However, this back-up ring is welded in place whereas the back-up ring of the present invention is free floating and is designed to slide and move to its actuation position, when pressurized. Finally, UK patent application GB 2175355A appears to pertain to an oil well structure for creating a seal. While a wedge is added to the structure to prevent extrusion of the seal as the parts are pressed together it includes no similar features with respect to those of the present invention.
Turning now to heat shield assemblies, U.S. Pat. No. 5,761,907 to Pelletier, et al., also assigned to the assignee of the present invention, pertains to a thermal gradient dispersing heat shield assembly and the metal insulating sleeve thereof serves a similar function to heat shield utilized in the present invention. However, this reference patent pertains to non-analogous art, namely by being used in a fuel nozzle used to inject fuel in a jet engine. This reference seems to suggest that this is an incremental improvement to a prior art structure that also contains a heat shielding structure. Air gaps are, in fact, included in many aerospace and non-aerospace parts to serve as thermal barriers. The insulating sleeve of the present invention works in combination with other components in the QDC to block both radiation and convective heat transfer that promotes the breakdown of the seals that leads to QDC failure. The two noted applications are vastly different, with the insulation characteristics being the only somewhat similar feature. Similarly, the structure in U.S. Pat. No. 6,149,075 to Moertle et al. pertains to a method and apparatus for shielding heat from a fuel nozzle stem, in a non-analogous art, and provides a complete void for reducing heat transfer. As already noted, the insulation sleeve in the present invention works in conjunction with other parts in the QDC to block radiation and convection heat from causing heat leaks.
None of the discussed prior art structures pertains to the combination of features used in the present invention to achieve the requirements set forth in the noted industry standards.